Steam heat - gurgling radiators on a cold system only

heatysteam

Hi - I've searched and searched, and haven't found anyone quite with this problem, so I'd appreciate some input (or any followup questions):

I'm in a house with a possibly 80 year old steam heat system. It's single pipe (with a return for the main big pipe going opposite the boiler), just about every radiator has it's own vertical pipe coming off of that (or coming off of a horizontal one). It's a two floor building.

There are three radiators on the 2nd floor furthest from the boiler - one has its own pipe (A), one has a pipe coming up (B) and then a tiny horizontal pipe to the next room (C). A and C are exhibiting this problem (as best I can figure it out);

When the system is cold, then the boiler starts, the steam is supposed to start coming up. Both radiators have a gurgling sound - I'm 95% sure there's water in both radiators at this point. After some amount of time (10 minutes-ish) the gurgling stops, and you everything sounds fine (steam coming out through the vent until it shuts off). Every cycle until the system is off for a while sounds fine. Then, if it goes cold for a while, repeat with the gurgling. (When gurgling, a radiator might spurt water through the vent but it's not common)

I've tried replacing vents on both of the radiators, and that doesn't seem to fix anything. The pitch seems fine, and a manual tilt doesn't affect anything. I can't quite reason why there would only be water in a cold system, unless the steam coming up is helping the previous condensed steam drain - but why might that be?

Another observation, maybe related - the sight glass jumps up by a few inches randomly in way that _may_ correspond with a return of trapped water.

Does anyone have any insight?

neilc

are the supply valves on the rads fully open ?
they need to be on one pipe systems,
and or,
do the rads lift at all?
is there slack and possible wrong pitched pipe under the floor?
and more or,
is the rad pitched to drain back to the supply valve?
the vent end should be slightly higher than the valve end

heatysteam

yes, all the valves are open as far as they will go.
the rads don't really lift. i can force a lift but it doesn't help, do you think pitching it more aggressively could help? the vent ends are higher if checking with a level.
under the floor is pretty much a vertical pipe, so i don't think that could have a pitching issue. those connect to a big pipe in the basement, which i don't suspect since no other (closer) radiators have issues.

i'm wondering if there could be a clog in the radiator itself near the vent. but why would it only work well if the system is already hot?

neilc

I tried,
post a picture of a rad that gurgles

LS123

Hello, I had a similar issue, it was related to pitch of the rad and small steam leak from the treads where the vent was connected... I am guessing it may be similar.... also I read in the forum somebody who had adjustable steam vent that was preventing condensation return to the return line. As per @neilc picture probably helpful.

bburd

A cold system develops more condensate as it heats up than a warm one.

Are your steam pipes insulated? Insulation will reduce the startup condensate load.

You might also try a slower vent on those problem radiators, which will reduce the rate of condensation as the system heats up.

retiredguy

You said that radiator "C" has a tiny horizontal pipe going to it. What is the size of that pipe and just where is it connected to the rest of the piping? If it too small, that could be where the problem lies.

ethicalpaul

There is a section of horizontal pipe probably in the floor below the gurgling radiators or possibly in the basement where water is pooling.

When the water is cold, it kills the steam going to that radiator 

after a time of steaming, the steam has heated the water enough that it has evaporated or it lets the steam pass. That is when you’ll see heat at the radiator 

you must find and eliminate the place where water collects. I had exactly the problem you describe (plus water hammer): https://forum.heatinghelp.com/discussion/167233/fixing-pitch-issues-in-old-house